The invention relates to a supercharged internal combustion engine for motor vehicles, comprising an exhaust gas turbosupercharger consisting of an exhaust gas turbine and a charging blower driven thereby; a charge pressure control valve arranged in the exhaust manifold of the internal combustion engine, responsive to the charge pressure of the charging blower, and regulating an exhaust gas bypass line bypassing the exhaust gas turbine; and optionally actuated performance control member regulating the passage cross section of the charging air line downstream of the charging blower; and a charging blower-coupled bypass line connecting the intake line of the charging blower to the charging air line, and opening upstream of the performance control member in the charging air line, said bypass line containing a blow-off valve actuated in response to the position of the performance control member in such a way that said blow-off valve is closed in all positions of the performance control member for which the passage is open.
A supercharged internal combustion engine comprising a charge pressure control valve mounted in the exhaust gas line of the engine, responsive to the charging blower charge pressure, and regulating an exhaust gas bypass line bypassing the exhaust gas turbine is known from German application (Offenlegungsschrift) No. 1,426,076. When a predetermined charge pressure is reached the charge pressure control valve opens the exhaust gas bypass line, and a fraction of the exhaust gases is blown off through the exhaust gas bypass line into the atmosphere, bypassing the exhaust gas turbine. No special safety means avoiding the development of excessive pressure when the charge pressure control valve is defective is provided in this supercharged internal combustion engine. A similar arrangement is shown in U.S. Pat. No. 4,202,176. The engine of this patent also has a bypass line interconnecting intake and charging air lines that is controlled by a blow-off (bleeder) valve for circulating the fresh air stream around the supercharging blower when the engine throttle valve is closed.
To limit the rpm of supercharged or nonsupercharged internal combustion engines, it is known to disconnect the ignition (German application--Offenlegungsschrift--No. 2,406,814). If a catalyst is used in such an engine to improve the exhaust gas emission, the catalyst is automatically destroyed by the unburnt fuel when the rpm is limited by turning off the ignition.
To limit the rpm of a supercharged or nonsupercharged internal combustion engine, it is known also to interrupt the fuel supply to the engine by stopping the fuel pump. But in this case, it has been found disadvantageous that the vehicle is braked abruptly on rpm limitation by interruption of the fuel supply, which is not very pleasant for the occupants of the vehicle, and may also be dangerous in some cases.
Thus, a principal object of the present invention is to provide a supercharged internal combustion engine with an exhaust gas turbosupercharger whose operation is optimized.
According to a perferred embodiment of the invention, this object is achieved by providing an engine as described in U.S. Pat. No. 4,202,176, with an additional bypass line coupled to the charging blower that connects the charging blower to the charging air line, and opens upstream of a performance control member (throttle) in the charging air line. The passage cross section of the bypass line and is controlled by at least one operating parameter of the internal combustion engine. An rpm tranducer and/or an electric charge pressure safety switch that is responsive to the charge pressure has been found especially suitable for use as the controlling operating parameter. The rpm transducer may be an ignition pulse transducer.
When an rpm transducer is used, the bypass line is opened by the solenoid valve as a predetermined rpm is reached, so that a fraction of the fresh air stream is deflected around the charging blower. When used, the catalyst is not damaged in this phase of the operation of the engine. The engine rpm drops in response to the dropping charge pressure, and the vehicle is not abruptly braked.
When a charge pressure safety switch set up to respond to a charge pressure slightly higher than that actuating the charge pressure control valve is used, the bypass line is opened by the solenoid valve when the charge pressure control valve fails and does not open when a predetermined charge pressure is exceeded. Consequently, a fraction of the fresh air stream is deflected around the charging blower, and the charge pressure cannot continue to increase.
When both an rpm transducer and a charge pressure safety switch are used in an internal combustion engine, the application of a solenoid valve according to the invention provides for an engine comprising both an excessive rpm protection means and a safety means for protection from excessive charge pressure. The above cited disadvantages are eliminated with these means.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.